Top-dressing nitrogen fertilizer rate contributes to decrease culm physical strength by reducing structural carbohydrate content in japonica rice oleh Wu-jun ZHANG, Long-mei WU, Yan-feng DING, Fei WENG, Xiao-ran WU, Gang-hua LI, Zheng-hui LIU, She TANG, Cheng-qiang DING, Shao-hua WANG